Warning lights of various descriptions are used in fixed situations and on vehicles to increase the visibility of possibly hazardous activities or situations. Warning lights are used on construction and repair vehicles, police and security vehicles, ambulances and fire response vehicles, and the like. Warning lights are usually flashed or operated in a manner which creates a flashing appearance, such as by actual or simulated rotation, to increase visibility of the warning light and to draw attention to the hazardous situation. Various standard colors are used to designate the type of vehicle a light is used on, such as: yellow or amber, sometimes white, for general caution on non-emergency and non-official vehicles; red to indicate official emergency response vehicles such as fire, ambulance, and often police; and blue to indicate police vehicles in some districts. Sometimes, combinations of lights of different colors are used for different functions on a particular vehicle, such as amber caution lights on a police car for use in a stop to assist a stranded motorist, in addition to red and/or blue rotating lights for law enforcement purposes.
In the past, many types of warning lights, particularly for vehicles, employed incandescent types of lamps. Although incandescent lamps have provided useful service for illumination and warning lights, there are some negative aspects to incandescent lamps. Incandescent lamps with evacuated glass envelopes are susceptible to breakage. The filaments used in such lamps are also vulnerable to breakage from shocks, vibration, and fatigue over time from thermal expansion and contraction. Incandescent lamps produce heat by the mechanism through which they produce light, namely electrical resistance.
Other illumination sources besides incandescent lamps have been considered and implemented for both illumination purposes and signaling or warning light purposes, such as ionized gas or gas discharge lights (xenon, halogen, etc.) and solid state lights, including light emitting diodes (LED's). Light emitting diodes are considerably less vulnerable to damage from shock and vibration than incandescent lamps and consume less electrical power for a comparable level of illumination. More recently, light emitting diodes have been developed which can be operated at illumination levels which meet the photometric standards required by regulations and industry standards for warning lights. However, operating light emitting diodes at high levels of illumination generates heat within the diodes, which results in a decrease in light output when the diodes are so heated. Light output from light emitting diodes also changes with fluctuations in the voltage of the power source which powers them. There is, thus, a need for a warning light arrangement using light emitting diodes which operates the diodes at a desirably high level of light output and at a consistent and predictable level of light output.